1. Field of the Present Invention
The present invention relates to a liquid composition for ink jet, an ink set for an ink jet, and an ink jet recording apparatus and a recording method therefor.
2. Description of the Related Art
An ink jet printer is an apparatus that discharges liquid or molten solid ink out of a nozzle, a slit, or a porous film onto a sheet of paper, a piece of cloth, or a film to record thereon. It is known to have such advantages as compactness, moderate price, and quietness. A piezo ink jet method using a piezoelectric element and a thermal ink jet method in which recording is curried out by applying thermal energy to ink and so on have been developed, and attempts have been made to increase printing speed and improve image resolution. Ink jet inks used in such ink jet recording methods include inks containing a water-soluble dye and inks containing a pigment. In particular, the inks that contain the pigment are excellent in water resistance and light resistance and are able to obtain image quality high in optical density, and thus, such variously developed. While the inks that contain a pigment as a color material have such advantages as mentioned above, these inks have disadvantages in that fixability of an image and scuff resistance property are poor. Development with the intention to establish compatibility between the image quality and the fixability and scuff resistance has been actively pursued.
For example, a recording liquid made of an aqueous medium containing a pigment, a polymer dispersant and a nonionic surfactant is disclosed in Japanese Patent Application Laid-Open (JP-A) No. 56-147871. Furthermore, the use of an AB or BAB block copolymer as a dispersant of the pigment is disclosed in U.S. Pat. Nos. 5,085,698 and 5,221,334.
Furthermore, a method of increasing image fixability by adding a surfactant in ink is disclosed in JP-A No. 55-65269. Moreover, in order to improve the scuff resistance and evenness of an image, ink containing a pigment, inorganic oxide colloid and a water-soluble solvent is disclosed in JP-A No. 9-286941.
On the other hand, ultraviolet curable ink technology is an example of technology that is widely used to improve the fixability, the scuff resistance and the drying property of screen ink and gravure ink. Although the screen ink and the gravure ink are generally oil-based, application of the ultraviolet curable ink technology of those oil-based inks to water-based ink jet ink has been studied. JP-A Nos. 5-186721 and 7-224241 can be cited as examples thereof. In these patent documents, the so-called one-pack type recording method in which a recording liquid contains an ultraviolet curable resin, a photopolymerization initiator and a color material is disclosed. On the other hand, the so-called two-pack type recording method in which an ink set having ink and a processing liquid containing an ultraviolet curable resin is used is disclosed in JP-A No. 8-218018. Furthermore, a two-pack type recording method in which the ink contains either a photopolymerization initiator or an ultraviolet curable resin and the processing liquid contains the other one is disclosed in JP-A No. 2000-119574.
As is mentioned above, in general, in the one-pack type recording method, a photopolymerization initiator and a polymerizable compound that can cause a polymerization reaction due to an initiation reaction of the photopolymerization initiator are contained in the ink jet recording ink containing a color material. Then, when ultraviolet light (UV) is irradiated after an image is formed with the ink jet recording ink, the polymerizable compound polymerizes and thereby forms a recorded image with the scuff resistance (recording method A).
On the other hand, examples of the two-pack type recording include a method in which each of a photopolymerization initiator and a polymerizable compound is contained separately in an ink or a processing liquid, the two are mixed on the recording medium when an image is formed, and ultraviolet light is irradiated thereto (recording method B).
Furthermore, a liquid composition that does not contain a color material but contains a photopolymerization initiator and a polymerizable compound is provided separately from recording ink that contains a color material (recording method C).
Since the recording method A is easy to introduce into recording apparatus, it is the most general method among oil-based ink technology. However, since the color material has ultraviolet absorptivity, the curing action is disturbed. Water-based UV ink is liable to be disturbed since the polymerizable compound is diluted with water. In particular, in the case of the pigment being used as the color material, there is a result such that only a surface of a recorded image is partially cured and an interior portion thereof is not cured. Accordingly, not only can the scuff resistance not be obtained, but also a coated layer of a surface peels, resulting, on the contrary, in deteriorating the scuff resistance.
The recording method B is advantageous from a viewpoint of long-term storage, since a polymerization reaction due to spontaneous decomposition of a photopolymerization initiator can be prevented from occurring. However, since the photopolymerization initiator and the polymerizable compound are mixed on the recording medium, the mixing is not sufficient, and a large amounts thereof remain unreacted, resulting in poor film strength and insufficiency scuff resistance.
On the other hand, in the recording method C, since an ink ingredient forming a recorded image and a liquid composition containing a curing ingredient act separately, no influence on the image quality occurs, and sufficient strength in the scuff resistance of the film can be exhibited. In particular, it is characterized in that an UV filter effect due to a color material does not occur.
In the existing technology of water-based ultraviolet curable ink, there are requirements to improve scuff resistance, cracks of the film, and adhesive property onto the recording medium. The recording method C has being improved, however, a further improvement is strongly demanded. Furthermore, the recording method C is demanded to improvement discharge stability.